The invention relates to a tensioning frame for tensioning stencils of metal foil or plastic film provided with perforations at their margin, especially for stencil printing, wherein a clamping device is disposed in the frame and operated by a pressure medium for displacing tensioning bars having hooking pins which enter the perforations in the stencil.
Tensioning frames of this kind have been disclosed in published German Patent Application No. DE 195 30 373 A1. There, however, it is disadvantageous that on each tensioning bar two tensioning cylinders operated by compressed air are disposed at a great distance apart. It has been found that when the stencil is stretched, the result is a flexing of the tensioning bar. The resulting distortions have an adverse effect, since the requirements for accuracy in the mounting of the stencil are very high, especially in the case of "on-contact" printing in the fine pitch range.
Published PCT Application No. WO 92/08616 discloses a tensioning frame in which a tensioning beam is displaced by means of a tube supplied with a pressure fluid to tension a stencil. A holding band is fastened to the tension beam and bears the hooking pins for gripping the stencil. This, however, has the particular disadvantage that the means for guiding the tension beam must be very complicated.
Published PCT Application No. WO 97/03833 discloses the operation of the tensioning means of a tensioning frame by pressurized tensioning tubes. Here, however, the functionality requires the arrangement of an additional spring system.